R Chitra
Articles written in Pramana – Journal of Physics
Volume 63 Issue 1 July 2004 pp 107-115
R R Choudhury R Chitra P U Sastry Amit Das M Ramanadham
Using the crystal structure, a comprehensive interpretation of the origin of ferroelectricity in the hydrogen bonded triglycine family of crystals is given. Our detailed analysis showed that the instability of nitrogen double well potential plays a driving role in the mechanism of the ferroelectric transitions in these crystals.
Volume 63 Issue 2 August 2004 pp 257-261
Zinc (tris) thiourea sulphate (ZTS): A single crystal neutron diffraction study
P U Sastry R Chitra R R Choudhury M Ramanadham
The crystal structure of ZTS has been determined by neutron diffraction with a final
Volume 63 Issue 2 August 2004 pp 263-269
Hydrogen bonding in oxalic acid and its complexes: A database study of neutron structures
R Chitra Amit Das R R Choudhury M Ramanadham R Chidambaram
The basic result of carboxylic group that the oxygen atom of the -OH never seems to be a hydrogen bond acceptor is violated in the cases, namely urea oxalic acid and bis urea oxalic acid complexes, where the hydroxyl oxygen atom is an acceptor of a weak N—H… O hydrogen bond. The parameters of this hydrogen bond, respectively in these structures are: hydrogen acceptor distance 2.110 Å and 2.127 Å and the bending angle at hydrogen, 165.6° and 165.8°. The bond strength around the hydroxyl oxygen is close to 1.91 valence units, indicating that it has hardly any strength left to form hydrogen bonds. These two structures being highly planar, force the formation of this hydrogen bond. As oxalic acid is the common moiety, the structures of the two polymorphs, α-oxalic acid and β-oxalic acid, also were looked into in terms of hydrogen bonding and packing.
Volume 63 Issue 2 August 2004 pp 363-368
Amit Das R Chitra R R Choudhury M Ramanadham
The native form of serum albumin is the most important soluble protein in the body plasma. In order to investigate the structural changes of Bovine serum albumin (BSA) during its unfolding in the presence of urea, a small-angle neutron scattering (SANS) study was performed. The scattering curves of dilute solutions of BSA with different concentrations of urea in D2O at pH 7.2 ± 0.2 were measured at room temperature. The scattering profile was fitted to a prolate ellipsoidal shape (
Volume 71 Issue 5 November 2008 pp 905-910 Neutron Diffraction
Thiourea-doped ammonium dihydrogen phosphate: A single crystal neutron diffraction investigation
A Jayarama M R Suresh Kumar S M Dharmaprakash R Chitra R R Choudhury
Thiourea-doped ammonium dihydrogen phosphate (TADP) exhibits nonlinear optical property and the second harmonic generation efficiency of these crystals is three times that of pure ammonium dihydrogen phosphate (ADP) crystal. In this context, the study of structural distortion in the thiourea-doped ADP crystal is significant, hence single neutron diffraction investigations were undertaken. The final 𝑅-factors are: $R[F^{2} > 2\sigma(F^{2})] = 0.11$, Goodness of fit $(S) = 1.15$. Though the dopant could not be located from the difference Fourier map, the cell parameters ($a = b = 7.531(3)$ Å, $c = 7.544(5)$ Å) were found to be significantly greater than that of pure ADP at RT ($a = b = 7.502(1)$ ̊Å, $c = 7.546(1)$ ̊Å). This indicates that the dopant concentration in the crystals is small but enough to bring changes in the overall average structure.
Volume 71 Issue 5 November 2008 pp 911-915 Neutron Diffraction
Single crystal neutron diffraction study of triglycine sulphate revisited
Rajul Ranjan Choudhury R Chitra
In order to get the exact hydrogen-bonding scheme in triglycine sulphate (TGS), which is an important hydrogen bonded ferroelectric, a single crystal neutron diffraction study was undertaken. The structure was refined to an 𝑅-factor of $R[F^{2}] = 0.034$. Earlier neutron structure of TGS was reported with a very limited data set and large standard deviations. The differences between the present and the earlier reported neutron structure of TGS are discussed.
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